The present invention relates to the production of tissue heart valves generally and more particularly to fixtures for use in conjunction with fixation of valve tissue.
Tissue heart valves may be fabricated by harvesting a mammalian aortic root including the aortic valve and thereafter fixing the harvested aortic root to crosslink the tissue. Thereafter, the aortic root may be trimmed and employed as heart valve for implantation in human beings. The valve may be mounted to a stent or frame, for example as disclosed in U.S. Pat. No. 5,824,069, issued to Lemole, U.S. Pat. No. 4,816,029, issued to Penney, et al., U.S. Pat. No. 5,716,401, issued to Eberhardt, et al. or U.S. Pat. No. RE 30,912, issued to Hancock. Alternatively, the valve may be implanted without an associated stent, as described in U.S. Pat. No. 5,336,258, issued to Quintero, et al or U.S. Pat. No. 6,074,419, issued to Healy, et al.
U.S. Pat. No. 5,824,060 issued to Christie, et al. and incorporated herein by reference in its entirety describes a process for heart valve fixation, in which the harvested aortic root is subjected to a fixative fluid to provide a first differential fluid pressure across the tubular wall of the outflow section of the aortic root and a second differential fluid pressure across the valve leaflets. As disclosed, the inflow and outflow sections of the aortic root are coupled to fluid couplings that are in turn coupled to sources of fixative fluid under pressure. The entire assembly is also placed in fixative fluid during the fixation process.
U.S. Pat. No. 5,830,239 issued to Toomes and incorporated herein by reference in its entirety describes an improvement to the process of the ""060 patent, in which only the outflow section of the aortic root is mounted to a fluid coupling and the inflow section of the root is blocked by a plug. The plug is provided with a tube or cannula having an inlet portion extending through the valve leaflets and an outlet opening located in the inflow section of the aortic root, allowing fixative fluid to flow through the valve so that fluid may be applied to both sides of the valve and to the inflow and outflow sections of the aortic root. The fluid coupling is coupled to a source of fixative and the entire assembly is placed in fixative during the fixation process. The process disclosed in the ""239 patent substantially simplifies the fixturing process as compared to the ""060 patent.
The present invention is an improvement to the process described in the ""239 patent, providing a way to control axial stretch of the aortic root during the fixation process. Because the stretch of the aortic root is controlled, the fixturing system and process of the present invention is intended to produce an increased yield as compared to the process in the ""239 patent.
The fixturing system of the present invention resembles that as described in the ""239 patent, in that only a single fluid coupling is employed, preferably part of an outflow plug coupled to the outflow section of the aortic root, and in that the inflow section of the aortic root is blocked by an inflow plug. However, in the present invention, the cannula or tube extending from the inflow plug extends through the valve all the way to the outflow plug. The tube smoothly slides into the outflow plug, allowing for adjustment of the relative positions of the inflow and outflow plug. The outflow plug preferably has a setscrew or other mechanism associated therewith for fixing the location of the inflow plug relative to the outflow plug. The tube is provided with a series of holes extending along of the tube and arranged to be located on both sides of the valve leaflets, so that a zero pressure differential across the leaflets can be achieved during fixation.
In use, the outflow section of the aortic root is preferably first coupled to the fluid coupling, which in the preferred embodiment of the invention is part of an outflow plug, around which the outflow section of the aortic root is mounted. The fluid coupling is then coupled to a source of compressed air to close the valve leaflets and a contour ring is placed around the inflow section of the aortic root. The aortic tissue at the end of the inflow section of the aortic root is then folded back over the contour ring and a length of plastic tubing is slid over the tissue and contour ring and is maintained in place, for example, by means of a cable tie. Other mechanisms for restraining the outflow section of the aortic root during fixation may be substituted for the contour ring or the contour ring might, in some embodiments, be attached without prior application of pressure to close the valve leaflets.
The apertured tube or cannula and the attached inflow plug are then inserted into the aortic root with the tube passing through the valve leaflets and engaging the fluid coupling. The inflow plug attached to the tube is located within the plastic tubing and attached to it by means of cable ties or the like, compressing the tubing around the inflow plug. The fluid coupling is then again attached to a source of compressed air, which is used to inflate the aortic root to a desired pressure and the setscrew is employed to fix the outflow plug to the tube, correspondingly stabilizing the relative location of the inflow and outflow sections of the aortic root and preventing excessive longitudinal stressing during fixation. The assembly is then moved to a fixative bath where the outflow plug is coupled to a source of fixative under pressure, and the assembly is placed into the fixative bath during the fixation process. On completion of fixation, the aortic root is removed and trimmed and may thereafter be mounted to an associated heart valve stent.